MaGICC Thick Disk I: Comparing a Simulated Disk Formed with Stellar Feedback to the Milky Way

TL;DR

This study compares a cosmological simulation of a Milky Way-like galaxy with actual observations, focusing on structure and chemical properties, revealing both similarities and differences such as a notably thicker disk in the simulation.

Contribution

It provides a detailed comparison between simulated and observed galactic disks, validating some observational proxies and highlighting differences like the very thick disk in the simulation.

Findings

Simulated galaxy has a thick disk (~1.5 kpc) not seen in the Milky Way.

Qualitative agreement in age and metallicity distributions between simulation and observations.

Mono-abundance populations are good proxies for age in most cases.

Abstract

We analyse the structure and chemical enrichment of a Milky Way-like galaxy with a stellar mass of 2 10^{10} M_sun, formed in a cosmological hydrodynamical simulation. It is disk-dominated with a flat rotation curve, and has a disk scale length similar to the Milky Way's, but a velocity dispersion that is ~50% higher. Examining stars in narrow [Fe/H] and [\alpha/Fe] abundance ranges, we find remarkable qualitative agreement between this simulation and observations: a) The old stars lie in a thickened distribution with a short scale length, while the young stars form a thinner disk, with scale lengths decreasing, as [Fe/H] increases. b) Consequently, there is a distinct outward metallicity gradient. c) Mono-abundance populations exist with a continuous distribution of scale heights (from thin to thick). However, the simulated galaxy has a distinct and substantive very thick disk (h_z~1.5 kpc), not seen in the Milky Way. The broad agreement between simulations and observations allows us to test the validity of observational proxies used in the literature: we find in the simulation that mono-abundance populations are good proxies for single age populations (<1 Gyr) for most abundances.